The present invention relates to an air intake device for a motor vehicle with a riding saddle, such as a motorcycle, a three-wheeled motor vehicle, or the like.
Motor vehicles with riding saddles or saddle seats for riders include an engine positioned generally in a central position in a longitudinal direction of a vehicle body below a main pipe which is a main component of a vehicle frame. An air cleaner is disposed behind the engine and in front of a rear wheel, and a carburetor is positioned in the vicinity of the engine, the air cleaner and the carburetor being connected by a connecting tube. The connecting tube has an air inlet end coupled to an outlet port defined in a front surface of an air cleaner casing. The connecting tube is located substantially centrally in a transverse direction of the vehicle body. An exhaust pipe extends rearwardly from the engine alongside of the vehicle body.
The foregoing basic layout of various intake and exhaust components for the engine is shared by most of motorcycles and three-wheeled motor vehicles, including off-road motorized cycles such as moto-crossers or trail motorbikes, for example. In the off-road motor vehicles, the exhaust pipe generally extends rearwardy from the engine at a position away from the ground and close to a lower surface of the saddle seat to avoid interference with objects on the ground. This exhaust pipe arrangement has a problem in that where a muffler connected to the exhaust pipe is positioned laterally of the air cleaner, the heat generated by the muffler tends to adversely affect the connecting tube which is part of an air intake path of the engine. More specifically, when the temperature of air drawn by the air intake path is caused to rise by the heat of the muffler, the air is expanded in volume and mixed with fuel in the carburetor, the air-fuel mixture being then introduced into an engine cylinder, with the result that the volumetric efficiency (.epsilon..sub..nu.) of the engine is decreased. The off-road motor vehicle requires its air cleaner to have a higher air cleaning capacity as compared with the on-road motor vehicle. With the foregoing conventional arrangement of components, the outlet port for supplying cleaned air from the air cleaner is defined in the front surface of the air cleaner casing. Where a cleaner element is cylindrical in shape, the axis thereof is directed longitudinally of the vehicle body, and the area of the cleaner element effective for cleaning air cannot be increased since the cleaner casing is narrow in the transverse direction of the vehicle body, making it difficult to increase the diameter of the cylindrical cleaner element.